1. Field of the Invention
This invention relates generally to a rotating heating roller of the type having a three phase core and more particularly to such a rotating roller which includes a circumferentially laminated tubular core provided within the jacket of the rotating roller, four circumferential yokes provided on the core at the positions where the core is equally divided into three equal sections when viewed in the axial direction of the core and at the positions where the core terminates, three windings provided on the leg core between the yokes.
2. Description of the Prior Art
In the process of continuous rolling of a sheet material, it is most important to keep temperature distribution on the rotating heating roller in order to apply a constant and uniform nipping pressure on a sheet material or a web material processed by the roller. The surface temperature of the roller is required to be uniform in order to avoid any defect of the quality of the treated products caused by the temperature difference on the surface of the roller.
In order to keep the surface temperature of a roller uniform, prior construction proposed to locate an iron core coaxial with the roller and to arrange an electromagnetic coil wound outside the core within the interior of the roller. In this construction, a magnetic flux is generated in the core along the direction of the axis of the roller inasmuch as the electromagnetic coil is excited by an alternating current source and the magnetic flux passes through a closed magnetic circuit which surrounds the periphery of the roller. An electromotive force is induced in the roller by the magnetic flux because the roller acts as a one-turn coil. An electric current is generated in the peripheral direction of the roller by the electromotive force and the roller is heated by the Joule's heat of the current.
In the prior art, when heat generation is needed in a rotating roller, a heat generating element is unevenly embeded within the rotating roller so that the surface temperature of the roller is made uniform in the direction along the axis of the roller. With this prior art construction of the roller, heat generation is not kept uniform when the heat generating element wears down with time.
In another prior art, the outer surface of a magnetic cylinder is tightly affixed to the inner surface of the roller and a copper ring is provided between gaps of the magnetic cylinder so as to control the secondary short circuit current that flows within the roller along the inner thereof and within the copper ring. With this prior construction of the roller, the surface temperature distribution is made better out the mechanism is very complicated.